Conversion of crude oil fractions to olefins

ABSTRACT

A catalytic process for hydrocracking crude oil fractions into a C 2  -C 5  alkane mixture having a normal paraffin to isoparaffin molar ratio greater than about 3:1 and thermally cracking this mixture to recover ethylene and propylene. 
     The hydrocracking catalysts used are made from a Group VIII metal, a Group VI B metal or mixtures thereof, with a halogen supported on a silica-alumina support or a natural or synthetic faujasite. The catalysts must be sulfided prior to or during use.

BACKGROUND OF THE INVENTION

The present invention relates to an improved process for convertingcrude oil fractions into an olefin product by hydrocracking the crudeoil fractions to C₂ - C₅ paraffins and thermally cracking these to aC₂ - C₃ olefin mixture.

It is known from U.S. Pat. No. 3,598,724 that C₃ - C₄ paraffins can beproduced from hydrocarbons boiling in the range from 100°F. to 550°F. byhydrocracking over a catalyst comprising mordenite mixed with anickel/tin catalyst supported on an amorphous inorganic oxide.

Similar patents such as U.S. Pat. No. 3,385,782 suggest thehydrocracking of high boiling hydrocarbon fractions into C₁ - C₄paraffins.

These prior art process, as well as U.S. Pat. No. 3,718,575, areprimarily concerned with the production of LPG or liquified petroleumgas (C₃ - C₄) useful as fuels and thus were interested mainly inproducing higher yields of C₃ - C₄ than the C₁ - C₂ yields.

SUMMARY OF THE INVENTION

It now has been discovered that by using a highly active catalyst,larger amounts of hydrogen and higher temperatures, it is possible tohydrocrack a crude oil fraction boiling in the range from 200° to1000°F. with substantially complete conversion into a C₂ - C₅ producthaving a normal paraffin to isoparaffin molar ratio ranging from about3:1 to about 6:1 and subsequently thermally crack this C₂ - C₅ productinto a C₂ - C₃ olefin mixture.

The advantage in having a high normal paraffin ratio in the C₂ - C₅product is that this product can be used as a replacement for L.P.G. asa feedstock to existing ethylene production facilities without extensiveand/or expensive modifications thereof.

A further advantage of the present invention is that whereas it is knownto thermally crack gas oils to olefins in yields of 30-35 pounds per 100pounds of feed, by using the present two-step invention it is possibleto obtain yields of 50-60 pounds per 100 pounds of feed.

In general the present invention comprises a process for the productionof ethylene and propylene as co-products which comprises:

A. hydrocracking a crude oil fraction boiling in the range from 200° to1000°F. by contacting a mixture of said fraction and hydrogen with ahighly active sulfided hydrocracking catalyst under pressure greaterthan about 400 psig wherein

1. the molar ratio of hydrogen to said fraction is in the range fromabout 4:1 to about 50:1;

2. the temperature range is from about 300° to about 565°C.; and

3. the residence time is from about one to about 180 seconds;

4. the sulfided catalyst comprises a Group VIII metal, a Group VI Bmetal, or mixtures thereof, and a halogen, supported on a catalystsupport of silica-alumina mixtures, or a natural or synthetic faujasite;

5. conditions (1) - (3) are selected so as to achieve a normal paraffinto isoparaffin molar ratio greater than about 3:1 in the hydrocrackedproduct;

B. separating the hydrocracked product of step

A. to recover a C₂ - C₅ alkane product,

C. thermally cracking the C₂ - C₅ product and

D. recovering ethylene and propylene as coproducts.

Preferably, the crude oil fraction used is a gas oil fraction boiling inthe range from 350°-800°F. and preferably the molar ratio of hydrogen tothe gas oil fraction is in the range from about 10:1 to about 30:1; thetemperature range is from about 450° to about 550°C.; and the residencetime is from about 5 to about 100 seconds.

DESCRIPTION OF THE INVENTION

In general, the present invention involves the hydrocracking ofhydrocarbon feedstocks boiling in the range from 200° to 1000°F. Theseinclude diesel fuel, light gas oil, heavy gas oil, lube oil, catalyticcycle oil, and coke oven oil.

The catalysts used in this invention are generally known from U.S. Pat.No. 3,268,437; U.S. Pat. No. 3,399,132; U.S. Pat. No. 3,617,485 andFrench Pat. No. 2,141,584. The disclosures of these patents areincorporated by reference herein. The catalysts used are furtherillustrated by preparations 1-3 hereinafter.

The operating conditions under which the above catalysts are used inthis invention for hydrocracking are a temperature range from about 300°to about 565°C. and preferably about 450° to about 550°C., a residencetime from 1 to 180 seconds and preferably 5-50 seconds, a range ofhydrogen to hydrocarbon molar ratio of from 4:1 to 50:1 and preferably10:1 to 30:1 and a pressure range from about 400 to 2000 psig andpreferably 500-900 psig.

It is to be understood that the conditions selected are chosen in orderto insure that the hydrocarbon feed is completely converted to produceC₂ - C₅ alkanes with a yield of 91-95% with only a 2-4% yield of methaneand 1-7% yield of C₆ - C₉ alkanes and with a normal paraffin toisoparaffin molar ratio greater than about 3:1.

As is known in the prior art, the catalysts may be sulfided by addingorganic or inorganic sulfur compounds to the feed material or thecatalyst may be sulfided during their preparation as is shown inPreparation 3 hereinafter.

A related aspect of the invention as hereinbefore mentioned is that thehydrocracked product can be fed to a thermal cracker operating under atemperature range from about 800° to about 925°C.; a pressure range fromabout 10 to 30 psig; a residence time range from about 0.1 to 1.0seconds and a steam/hydrocarbon ratio of about 0.1 to about 1.0 lb.steam/lb. hydrocarbon to produce an ethylene-propylene product.

The following examples are presented to further illustrate but not limitthe invention.

Preparation 1 -- Preparation of 6% Ni, 19% W, 2% F on Si0₂ -A1₂ 0₃

The support for the catalyst was 1/8 inches extrudates composed of 25%A1₂ 0₃ and 75% Si0₂. 119.5 gm. of this support was dried forapproximately 16 hours in an oven at 115°C.

A solution was prepared by dissolving 47.4 gm. of Ni(NO₃)₂ .6H₂ 0 in 40ml. deionized water and dissolving 44.4 gm. (NH₄)₆ W₇ 0₂₄ .6H₂ 0 in 40ml. deionized water. The two solutions were mixed and the volumeadjusted to 113 ml. with the addition of deionized water. This solutionwas poured slowly (while stirring) over the dried support.

The catalyst was dried for approximately 16 hours at 115°C. and was thencalcined in a muffle furnace at 550°C. for 5 hours.

4 ml. of 48% hydrofluoric acid was diluted to 100 ml. with deionizedwater and the solution was poured slowly over the calcined catalystuntil all of the solution was adsorbed. The catalyst was dried at 115°C.for 3 hours and calcined at 550°C. for 5 hours. Surface area of thecatalyst was 162 m² /gm.

Preparation 2 -- Preparation of 6% Ni, 19% W, 2% F on Rare EarthExchanged Y-Zeolite

239 gm. of Linde SK-500 catalyst (a Y-zeolite exchanged with 10% rareearth mixture) was dried for approximately 16 hours at 200°C. in aflowing stream of nitrogen.

94.7 gm. Ni(N0₃)₂ .6H₂ 0 and 88.8 gm. (NH₄)₆ W₇ 0₂₄ .6H₂ 0 was dissolvedin deionized water and the final volume of the solution was adjusted to150 ml. by addition of deionized water. This solution was poured slowlyover the zeolite. The mixture was stirred until all of the liquid wasadsorbed. The catalyst was dried for 2 hours at 155°C. and then calcinedat 500°C. for 2 hours.

8 ml. of 48% hydrofluoric acid was diluted to 100 ml. and was pouredslowly over the calcined catalyst until all of the solution wasadsorbed. The catalyst was dried at 115°C. for 2 hours and calcined at500°C. for 2 hours. Surface area of the catalyst was 275 m² /gm.

Preparation 3 -- Catalyst sulfiding Procedure

The catalysts were loaded into a 1 inch stainless steel tube reactor anddried at 400°C. and atmospheric pressure using a nitrogen flow of 1liter per minute. Catalyst temperature was reduced to 50°C. and thenitrogen flow stopped. The sulfiding gas mixture was passed over thecatalyst at a gas hourly space velocity of 680. This gas mixture was 10%hydrogen sulfide and 90% hydrogen.

As the hydrogen sulfide reacted with the catalyst the temperatureexothermed. After the exotherm passed through the bed the temperaturewas held at 50°C. for 30 minutes and then was slowly raised to 325°C. Itwas held at 325°C. for two hours. At this point the sulfiding of thecatalyst was complete.

Example 1 -- Conversion of Gas Oil to Ethylene and Propylene

An experiment was conducted in which a gas oil was hydrocracked and theproducts were passed through a thermal cracker to produce ethylene andpropylene. The hydrocracker consisted of a 1 inch O.D. stainless steeltube reactor 12 inches long loaded with 100 ml. of the catalyst ofPreparation 1. The catalyst was sulfided according to the sulfidingprocedure of preparation 3. A gas oil having a boiling point range from350° to 500°F. was preheated and passed over the catalyst at a rate of0.84 m/min which corresponds to a liquid hourly space velocity (LHSV) of0.5. Hydrogen was mixed with the gas oil prior to entering the preheaterat a rate of 2.46 liters per minute. The reactor temperature was 550°C.at a pressure of 600 psig. The H₂ /hydrocarbon molar ratio was 30/1.Hydrocarbon product from the hydrocracker reactor was composed of 4.0%CH₄, 5.9% C₂ H₆, 35.9% C₃ H₈ , 18.4% normal butane, 16.0% isobutane,5.8% normal pentane, 8.7% isopentanes, and 5.3% C₆ - C₉ paraffins.

The entire product from the hydrocracker, including hydrogen was passeddirectly into a laboratory thermal cracker whose inlet temperature was500°C. The residence time was 0.5 sec., pressure was 15 psig, and theoutlet temperature was 890°C. From this overall process the yield ofeach component was as follows: C₂ H₆ -- 16.4%, C₂ H₄ -- 38.1%, C₃ H₈ --0.5%, C₃ H₆ -- 2.0% and the remainder methane and C₄ + paraffins.

Better yields are obtained if the hydrogen, methane, and the C₆ - C₉components are separated from the C₂ - C₅ fraction. The C₂ - C₅ fractionis then mixed with steam in a ratio of 0.3 lb. steam/lb. C₂ - C₅ andinjected into the thermal cracker.

Examples 2-4 -- Effect of Temperature on the Molar Normal/Iso ParaffinRatio and on the Percent C₂ - C₅ in the Product from the Hydrocracker

    Temp.      Press.  Molar    Wt.% in Product                                   Example                                                                              °C.                                                                            psig    n/i    CH.sub.4                                                                            C.sub.2 -C.sub.5                                                                     C.sub.6 -C.sub.9                   ______________________________________                                        2      400     600     0.87   0.36  66.8   32.7                               3      450     600     1.49   0.72  77.1   22.2                               4      500     600     5.37   3.20  89.2    7.6                               ______________________________________                                    

All examples were over sulfided 6% Ni, 19% W, 2% F on a Si0₂ -A1₂ 0₃support at LHSV of 1.0, H₂ /HC molar ratio of 30/1 and with a conversionof 100% following the procedures of Example 1. The feedstock was 50%hexadecane and 50% 2,6,10,14-tetramethyl pentadecane.

These examples show that at lower temperatures the desired high molarratio of normal to isoparaffins (n/i) is not achieved while at highertemperatures the production of methane begins to become excessive.

Examples 5-6 -- Effect of Sulfur on Methane Formation

    Exam-                                                                             Temp.                                                                             Press.                                                                             Molar                                                                             Wt.% in Product                                              ple °C.                                                                        psig n/i CH.sub.4                                                                          C.sub.2 -C.sub.5                                                                   C.sub.6 -C.sub.9                                                                   Comments                                       __________________________________________________________________________    5   550 600  --  99.6                                                                              0.4  0    unsulfided catalyst                            6   550 600  3.55                                                                               4.0                                                                              90.8 5.0  sulfided catalyst                                                             (about 2.0% sulfur)                            __________________________________________________________________________

Both examples were over 6% Ni, 19% W, 2% F on SiO₂ -A1₂ 0₃ with andwithout sulfur at LHSV of 0.5, H₂ /HC molar ratio 32/1, and with aconversion of 100% following the procedures of Example 1. The feedstockwas a gas oil with a boiling point range of 350°-500°F., averagemolecular weight of 190, and 7 ppm sulfur.

These examples show that without a sulfided catalyst the feedstockconverts almost totally into methane.

Examples 7-9 -- Effect of High Temperature (Excessive CH₄ Formation

    Exam- Temp.    Press.  Molar  Wt.% in Product                                 ple   °C.                                                                             psig    n/i    CH.sub.4                                                                            C.sub.2 -C.sub.5                                                                     C.sub.6 -C.sub.9                   ______________________________________                                        7     500      600     2.95   2.6   75.1   21.2                               8     550      600     6.09   6.7   71.2   21.2                               9     610      600     19.96  20.4  67.6   11.5                               ______________________________________                                    

All examples were over sulfided 6% Ni, 19% W, 2% F on Si0₂ -A1₂ 0₃ atLHSV of 1.0, H₂ /HC molar ratio of 30/1, and with a conversion of 100%following the procedures of Example 1. The feedstock was a gas oil witha boiling point of 260°-680°F., average molecular weight 200, and 0.26weight percent sulfur.

These examples show that at temperatures over about 565°C., excessamounts of undesired methane are obtained.

Examples 10 and 11 -- Effect of Fluorine Addition to Catalyst on % C₂ -C₅ in Hydrocracker Product

    Temp.     Press.                                                                             Molar                                                                              Wt. % in Product                                          Example                                                                            °C.                                                                         psig n/i  CH.sub.4                                                                          C.sub.2 -C.sub.5                                                                   C.sub.6 -C.sub.9                                                                   Comments                                    __________________________________________________________________________    10   550  600  3.10 4.3 83.8 11.3 No flourine                                 11   550  600  3.55 4.0 90.8 5.0  2% fluorine                                 __________________________________________________________________________

Both examples were over sulfided catalysts containing 6% Ni, 19% W, on aSiO₂ -A1₂ 0₃ support with and without 2% fluorine at LHSV of 0.5, H₂ /HCmolar ratio 32/1, and with a conversion of 100% following the proceduresof Example 1. The feedstock was a gas oil with a boiling point range of350°-500°F., average molecular weight of 190, and 7 ppm sulfur.

These examples show a more acidic catalyst increases the yield of thedesired C₂ - C₅ product and decreases the C₆ - C₈ component. Similarresults are obtained with chlorine, bromine and iodine.

Example 12 -- Conversion of Gas Oil to C₂ - C₅ Paraffins

An experiment was conducted in which a gas oil was hydrocracked toproduce a paraffinic product in the C₂ - C₅ range. The hydrocrackerconsisted of a 1 inch O. D. tube reactor 12 inches long loaded with 200ml. of the catalyst of Preparation 2. The catalyst was sulfidedaccording to the sulfiding procedure of Preparation 3. Gas oil having aboiling point range of 290° to 685°F., an average molecular weight of220, and a sulfur content of 0.18 wt.% was preheated and passed over thecatalyst at a rate of 1.68 ml/min. which corresponds to a liquid hourlyspace velocity of 0.5. Hydrogen was mixed with the gas oil, prior toentering the preheater, at a rate of 4.74 liters/min. The reactortemperature was 475°C. at a pressure of 600 psig. The H₂ /hydrocarbonmolar ratio was 28/1. The hydrocarbon product from the hydrocrackerreactor was composed of 3.1% CH₄, 7.7% C₂ H₆, 40.3% C₃ H₈, 17.7% n-C₄H₁₀, 15.4% i-C₄ H₁₀, 4.1% n-C₅ H₁₂, 5.9% i-C₅ H₁₂ and 5.8% C₆ - C₉hydrocarbons. The conversion was 100%.

The above hydrocarbon product is then thermally cracked as in Example 1to produce an ethylene-propylene product.

We claim:
 1. A process for the production of an ethylene-propyleneproduct which comprises:A. hydrocracking a crude oil fraction boiling inthe range from 200° to 1000°F. by contacting a mixture of said fractionand hydrogen with a highly active sulfided hydrocracking catalyst undera pressure greater than about 400 psig wherein1. the molar ratio ofhydrogen to said fraction is in the range from about 4:1 to about 50:1;2. the temperature range is from about 300° to about 565°C.; and
 3. theresidence time is from about one to about 180 seconds;
 4. the catalystcomprises of Group VIII metal, a Group VI B metal, or mixtures thereofand a halogen supported on a catalyst support of silica-aluminamixtures, or a natural or synthetic faujasite;
 5. conditions (1) - (3)are selected so as to produce a C₂ - C₅ product in a yield of 91- 95%and to achieve a normal paraffin to isoparaffin molar ratio greater thanabout 3:1 in the C₂ - C₅ portion of the hydrocracked product; B.separating the hydrocracked product of step (A) to recover a C₂ - C₅alkane product; C. thermally cracking the C₂ - C₅ product and D.recovering ethylene and propylene as co-products.
 2. The method of claim1 wherein the crude oil fraction is a gas oil boiling in the range from350°-800°F.
 3. The method of claim 2 wherein1. the molar ratio ofhydrogen to said fraction is in the range from about 10:1 to about 30:1;2. the temperature range is from about 450° to about 550°C.; and
 3. theresidence time is from about 5 to about 50 seconds.
 4. In a process forthe production of an ethylene-propylene product wherein a crude oilfraction boiling in the range from 200° to 1000°F. is hydrocracked witha highly active sulfided hydrocracking catalyst under a pressure greaterthan about 400 psig and the hydrocracked product is thermally cracked toyield an ethylene-propylene product, the improvement which comprisescontacting the crude oil fraction with hydrogen in a molar ratio ofhydrogen to said fraction in the range from about 4:1 to 50:1 at atemperature range from about 300° to about 565°C. with a residence timeranging from about 1 to about 180 seconds so as to produce a C₂ - C₅product in a yield of 91- 95% and to achieve a normal paraffin toisoparaffin molar ratio greater than about 3:1 in the C₂ - C₅ portion ofthe hydrocracked product.
 5. The process of claim 4 wherein the crudeoil fraction is a gas oil boiling in the range from 350° to 800°F. 6.The process of claim 5 wherein the molar ratio of hydrogen to said gasoil is in the range from about 10:1 to about 30:1, the temperature rangeis from about 450° to about 550°C. and the residence time is from about5 to about 50 seconds.
 7. A process for the production of anethylene-propylene product which comprises:A. hydrocracking a crude oilfraction boiling in the range from 200° to 1000°F by contacting amixture of said fraction and hydrogen with a highly active sulfidedhydrocracking catalyst under a pressure greater than about 400 psigwherein1. the molar ratio of hydrogen to said fraction is in the rangefrom about 4:1 to about 50:1;
 2. the temperature range is from about300° to about 565°C.; and
 3. the residence time is from about one toabout 180 seconds;
 4. the catalyst comprises a Group VIII metal, a GroupVI B metal, or mixtures thereof supported on a catalyst support ofsilica-alumina mixtures, or a natural or synthetic faujasite; 5.conditions (1) - (3) are selected so as to produce a C₂ - C₅ product ina yield of 91-95% and to achieve a normal paraffin to isoparaffin molarratio greater than about 3:1 in the C₂ - C₅ portion of the hydrocrackedproduct;B. separating the hydrocracked product of step (A) to recover aC₂ - C₅ alkane product; C. thermally cracking the C₂ - C₅ product and D.recovering ethylene and propylene as co-products.
 8. The method of claim7 wherein the crude oil fraction is a gas oil boiling in the range from350°-800°F.
 9. The method of claim 8 wherein1. the molar ratio ofhydrogen to said fraction is in the range from about 10:1 to about 30:1;2. the temperature range is from about 450° to about 550°C.; and
 3. theresidence time is from about 5 to about 50 seconds.